<!DOCTYPE html>
<html lang="en">
    <head>
        <meta charset="UTF-8">
        <meta name="viewport" content="width=device-width, initial-scale=1.0">
        <title>QQ</title>

        <style type="text/css">
            body { margin: 0 ; padding: 0 ; }
            h3 { text-align: center ; }

            .wrapper { height: 800px ; line-height: 800px ; text-align: center ; font-size: 200px ;  border: 1px dotted blue ; }

            .odd { background-color: #dedede ; }
            .even { background-color: #ffff00 ; } 

            .second {
                /*
                background-image: url(fisrtbg.jpg) ;
                background-repeat: no-repeat ;
                background-position: center ;
                background-size: cover ;
                background-attachment: fixed ;
                */
                background: #ffff00 url(fisrtbg.jpg) center no-repeat  fixed ;
                background-size: contain ;
            }

            .fourth {
                /*
                background-image: url(secondbg.jpg) ;
                background-repeat: no-repeat ;
                background-position: center ;
                background-size: cover ;
                background-attachment: fixed ;
                */
                background: #ffff00 url(secondbg.jpg) left top/80% 50% no-repeat fixed;
            }

            .sixth {
                background-image: url(thirdbg.jpg) ;
                background-repeat: no-repeat ;
                background-position: center ;
                background-size: cover ;
                background-attachment: fixed ;
            }

        </style>
    </head>
    <body>

        <div class="wrapper odd first">first</div>

        <div class="wrapper even second">second</div>

        <div class="wrapper odd third">third</div>

        <div class="wrapper even fourth">fourth</div>

        <div class="wrapper odd fifth">fifth</div>

        <div class="wrapper even sixth">sixth</div>

        <div class="wrapper odd seventh">seventh</div>
        
    </body>
</html>